478 



ELECTRICITY. 



uu. 



" the other, as sofli M one of thrm touched the eel, the 



her hu\ing his hand in the water near it, they r, 

 t ved a shock. This experiment wa repeated l."> 

 jumj,,, times witli \... en. When tin- distance nl'the 



the ihitil- wires was one-fiftieth of an inch, the shock never |>i-- 

 ^ ** l>c ^ ' *ed between them. Dr Williamson, however, was ne- 

 \tr al'le to set- the olei-tric spark between the two me- 

 tallic points, which he ascribed to the bail state of health 

 nf hi- gymnotus. Mr \Val-h repeated this experiment 

 in a different manner. He applied to a piece of glass a 

 sheet of pewter, in which he had left a sin. ill separation 

 or slit. 1'liis slicct had its two edges in communication 

 ^^ witlit he body, through which t he electricity of the fish was 

 discharged. At the instant of the discharge, lie pem-i- 

 STfa ihe*" vct * *" e l t>ctr > c simrk, which went beyond the little in- 

 fymBMvu. tcrval made in the sheet. The success of this experi- 

 ment depends on the fish being in the open air ; for 

 when it is immersed in water, the spark is not visible. 

 II. Humboldt observed when he was in South Ameri- 

 ca, that the gymnotus gave the most frightful shock*, 

 without making any external motion of the eyes, hea.l, 

 or fins, like the torpedo. 



The preceding experiments were made upon a gym- 

 notu- kept in a Targe vessel, and supported by pieces of 

 dry timber about 3 feet above the floor. A small hole 

 was bored in the vessel, and when any person provoked 

 the eel, another person holding his finger in the stream 

 running through this hole received the shock. From 

 the different experiments which he made, Dr William- 

 son concludes, that the gymnotus has the power of 

 communicating a painful sensation to animals that touch 

 or come near it ; that this effect depends solely on the 

 will of the eel ; that it has the power of giving a small 

 shock, a severe one, or none at all ; that the shock does 

 not depend on the muscular action of the eel, but has 

 the same effect as that produced by common electricity. 

 Expkna- In order to convey to our readers an idea of the strue- 



' t ~ ture of the gymnotus, we have given a representation 

 of it in Plate CCXLVI. Fig. 2. where the skin is remo- 

 v ed to shew the electrical organs. The lower surface 

 r.ATE of the head is shewn at A ; the cavity of the belly at 

 'CXJ.VI. B ; the anus at C ; the fin at D ; the back of the fish, 

 when the skin has not been removed, at E ; the fin 

 wliich extends along the lower edge of the fish at FF ; 

 H, H, H, are the lateral musclea of the above fin, re- 

 moved and carried back with the skin to expose the 

 small organs; I is part of the muscle left in its place ; 

 KKK is the large electrical organ ; LLL the small elec- 

 trical organs ; m m m the substance which separates the 

 large organ from the small one ; and n the place where 

 this substance is removed. 



Hunter's From a minute examination of the electrical organs 

 Wrvtiun of the gymnotus, Dr Hunter found, that they occupy 

 on the die- nearly one half of that part of the flesh in which they 

 ]"* are P' acc< '> alu ' constitute perhaps more than one-third 

 '" of the whole fish. The animal possesses two pair of 

 electrical organs of different sizes, and placed on diffe- 

 rent sides. The large organ KKK occupies the whole 

 of the lower and the lateral part of the body, constitu- 

 ting the thickness of the fore part of the animal, and 

 stretching from the abdomen to near the end of the tail, 

 where it terminates almost in a point. The two organs 

 are separated at the upper part by the muscles of the 

 back, at the middle part by the air bag, and at the lower 

 }iart hy the middle partition. The small organ extends 

 along the lower edge of the animal almost as far as the 

 other, terminating almost insensibly near the end of the 

 tail. The two small organs are separated from one ano- 

 ther by the middle muscle, and by the bonea in which 



the fins are articulated. In order to perceive the large Dctipi 

 organ, it is necessary merely to remove ilie skin, \vhici 

 adhere^ to it by a loose cellular membrane ; but in order " ~""~ 

 to perceive the small organ, we '11111-1 remove tin- l<mg 

 row nt' small muscle* which mo\e the fin. .in 



consist of two parts \i.'.. flat partitions >.. ml 



cross divisions between them. Ti i are very 



thin and tender membranes placed parallel to one ano- 

 ther; they stretch in the direction of the length of the 

 (Mi : and having their breadth nearly equal to the semi- 

 diameter of the animal's body, the length of the septa 

 are different, some of them being as long as tlio whole 

 body. The distances between tin- -epta vary with the 

 size of the fish. In one two feet four inches long, their 

 distance was nearly ^ of an inch ; and in the bro. 

 part of the organ, which was an inch and a quarter, 

 there were 34 septa. The small organ has the same 

 kind of septa, but they stretch in a direction some- 

 what serpentine. Their distance is only about ,'.tli 

 part of an inch ; and in the breadth of the organ, which 

 is half an inch, there are fourteen septa. Mr Hunter is 

 of opinion, that the septa answer the same purpose as 

 the columns in the torpedo, forming walls or abutment* 

 for the subdivisions, and constituting so many distinct 

 organs. These septa are intersected transversely by 

 very thin plates or membranes, whose breadth is the 

 distance between any two septa, and therefore of diffe- 

 rent breadths in different parts; broadest at the edge, 

 which is next to the skin ; and narrowest at that next to 

 the centre of the body, or to the middle partition which 

 divides the two organs. The lengths of these mem- 

 branes are equal to the breadths of the septa between 

 which they are situated, and there is a regular series of 

 them from one end of any two septa to the other end. 

 In one inch, there are no fewer than 240 of these trans- 

 verse membranes. 



The gymnotus examined by Dr Hunter was not of a 

 large size. Dr Garden saw one 3 feet 8 inches long ; 

 and Dr Bancroft was told when he was at Guiana, that 

 some of these fish have been seen in the Surinam river 

 upwards of 20 feet long, whose shock proved immedi- 

 ately fatal to those who received it. 



Redi, Perrault, and Lorenzini, believed that the elec- 

 tricicity of the torpedo was owing to the emission of 

 an infinite number of corpuscles continually proceeding 

 from the fish, and which, by penetrating animal bo- 

 dies, benumbed them by their accumulation. It was 

 the opinion of Borelli, tliat it communicated a trem- 

 bling to the nerves, which deadened the member in 

 which it was produced. The most extraordinary no- 

 tion, however, was that of Schilling, who imagined n {j 

 that he hat! discovered sensible magnetic effects in theeleceri. 

 the gymnotus. He maintains, that when this eel was cal effects f 

 placed near a loadstone, it was attracted by it, and diegymm*. 

 adhered to it ; and became so languid when separa- tu- 

 ted from the loadstone, that it might be touched with 

 impunity. He observes, also, that the loadstone which 

 he used appeared to be covered with particles of iron ; 

 and that, when the fish was placed in water containing 

 iron filings, it became lively and vigorous. These ex- 

 periments were carefully repeated by Ingenhouz and 

 Spallanzani, who were unable to perceive any such 

 magnetical effects. M. Hahn, professor of medicine 

 at I.cyden. remarks, that the rivers in America in 

 which the gymnotus is found, carry along in their cur- 

 rent a magnetic sand ; and he supposes, that grain* of 

 this sand adhering to the glutinous skin of the fish, 

 might have been the cause of the illusions by which 

 Schilling was misled in bis experiments. 



